The invention relates to a method for measuring a semiconductor structure, with the semiconductor structure comprising an emitter and a base, and being a solar cell or a precursor of a solar cell.
In semiconductor structures for example based on an indirect semiconductor, such as silicon, it is known to obtain information, concerning the physical features of the semiconductor structure based on a luminescence radiation created in the semiconductor structure. In particular, measurements of the luminescence radiation are used to determine spatially resolved electric parameters in a semiconductor structure, which is a solar cell or a precursor of a solar cell and comprises at least an emitter and a base.
Here, it is known to determine the diffusion length of the semiconductor material from the measurement of the luminescence radiation, such as described in Wiirfel, P. et al., “Diffusions lengths of silicon cells from luminescence images”, Journal of Applied Physics, 2007, 101 (123110): p. 1-10.
In order to characterize solar cells, particularly to control the quality of industrially produced solar cells, it is desired to determine additional spatially resolved electric parameters, particularly the dark saturation current, the resistance of the emitter layer, and the local series resistance.
In luminescence radiation essentially created by impinging the semiconductor structure with an excitation voltage (so-called “electro-luminescence radiation”) it is known to determine the dark saturation current from two spatially resolved measurements of the electro-luminescence under different measuring conditions. Such a method is described in M. Glatthaar, J. Giesecke, M. Kasemann, J. Haunschild, M. The, W. Warta, and S. Rein, Journal of Applied Physics 105, 113110/1-5 (2009). However, this measuring method is disadvantageous in that, for example, the resistance of the emitter layer must be known and furthermore it must be spatially constant. In particular in industrially produced solar cells the resistance of the emitter layer frequently varies over the surface of the solar cell so that the above-mentioned conditions are not fulfilled. Furthermore, the method requires an extended measuring period so that it cannot be used in-line within a production process.